Propulsion device for proximity twin-screw vessel having shaft bracket and ship

ABSTRACT

A propulsion device for a ship includes a port propeller and a starboard propeller, a rudder disposed at a center in a vessel widthwise direction, and shaft brackets installed in front of the port propeller and the starboard propeller, respectively, and configured to rotatably support propeller shafts of the port propeller and the starboard propeller, wherein a distance between a front end of a propeller blade of the port propeller and a front end of a propeller blade of the starboard propeller at the center in the vessel widthwise direction is larger than 0 m and equal to or less than 1.0 m, and a rotational direction of the port propeller and the starboard propeller becomes an outer track rotating outward from the center in the vessel widthwise direction over the port propeller and the starboard propeller.

TECHNICAL FIELD

The present invention relates to a propulsion device for a proximitytwin-screw vessel having a shaft bracket, and a ship.

Priority is claimed on Japanese Patent Application 2014-233258, filedNov. 18, 2014, the content of which is incorporated herein by reference.

BACKGROUND ART

A propulsion device of a ship generally obtains a propulsive force byrotating a propeller using a main engine.

In the case of a ship known as a single screw vessel including one mainengine and one propeller, when the ship is increased in size, a loadlevel applied to the one propeller is increased. In order to obtain asufficient propulsive force, a rotational speed of the propeller shouldbe increased or a diameter of the propeller should be increased.Accordingly, since a circumferential speed of the propeller isincreased, a pressure in the vicinity of a propeller blade end islowered, and cavitation that is a phenomenon in which bubbles aregenerated in water may excessively occur. When cavitation occurs, thehull is vibrated through the stern and the bottom of the ship. Inaddition, erosion occurs in the propeller due to the cavitation andexerts a bad influence on durability of the propeller.

Here, it is known that the above-mentioned problems can be solved in aship known as a twin-screw vessel including two main engines and twopropellers. In a twin-screw vessel, a load level per propeller can bereduced to improve propeller efficiency, and cavitation can besuppressed.

As examples in which two propellers are disposed at the stern, anoverlapping propeller (OLP) type, an interlock propeller type, a type inwhich propellers are arranged at left and right sides in parallel, andso on, are provided.

Among these, in the OLP type, the two propellers are disposed to bedeviated at front and rear sides thereof, and at least portions of thetwo propellers when seen from the stern are disposed to overlap eachother. The propulsion performance can be improved by 5 to 10% than thesingle screw vessel by employing the OLP type.

In the interlock propeller type, a blade of the other propeller isdisposed to enter between blades of one propeller.

In the type in which the propellers are arranged at left and right sidesin parallel, the propellers are disposed at the same position in avessel longitudinal direction in parallel.

CITATION LIST Patent Literature

-   [Patent Literature 1] PCT International Publication No.    WO2006/095774

SUMMARY OF INVENTION Technical Problem

However., when the OLP type is used, the propeller disposed at the rearside alternately passes through a fast flow accelerated by the frontpropeller and a slow flow in the vicinity of a center in a vesselwidthwise direction (a widthwise direction of the vessel) during onerotation. For this reason, a load applied to propeller blades of therear propeller is largely varied. As a result, in the twin-screw vesselusing the OLP type, in comparison with the single screw vessel, abearing force applied to a bearing of a propeller shaft of the rearpropeller may become excessive.

In addition, since a rotational flow having a high velocity is newlyformed by rotation of the front propeller, the rear propeller should beoperated in an extremely complicated flow, which widens a range in whichcavitation occurs. As a result, excessive vibration may be generated.Further, when tip vortex cavitation (blade end vortex cavitation) occursfrom front ends of propeller blades of the front propeller, erosion mayoccur in the propeller blades due to burst of the generated bubbles onpropeller blade surfaces of the rear propeller.

In addition, in the case of the interlock propeller type, rotation ofboth of the propellers should be controlled such that the blades of onepropeller and the blades of the other propeller do not interfere witheach other and roll control becomes difficult. In to addition, in theworst case, when the blades of one propeller interfere with the bladesof the other propeller, the propeller may be damaged.

The present invention is directed to provide a propulsion device for aproximity twin-screw vessel having a shaft bracket and a ship that arecapable of improving propulsion performance while suppressingcavitation, erosion, or the like.

Solution to Problem

According to a first aspect of the present invention, there is provideda propulsion device for a proximity twin-screw vessel having a shaftbracket, the propulsion device includes: a port propeller and astarboard propeller installed at a stern hull; one rudder disposed at acenter in a vessel widthwise direction of the stern hull or two ruddersconstituted by a port rudder and a starboard rudder in rear of the portpropeller and the starboard propeller; and shaft brackets installed infront of the port propeller and the starboard propeller, respectively,and configured to rotatably support propeller shafts of the portpropeller and the starboard propeller, wherein a distance between a tipend of a propeller blade of the port propeller and a tip end of apropeller blade of the starboard propeller at a center in the vesselwidthwise direction is larger than 0 in and equal to or smaller than 1.0m, and a rotational direction of the port propeller and the starboardpropeller becomes an outer track rotating from the center in the vesselwidthwise direction toward the outside over the port propeller and thestarboard propeller.

In this way, since the starboard propeller and the port propeller aredisposed to approach the vicinity of the center in the vessel widthwisedirection (referred to as the proximity twin-screw type), a longitudinalvortex in the vicinity of the center in the vessel widthwise directioncan be efficiently recovered, and propulsion performance can beimproved. In addition, the starboard propeller and the port propeller donot interfere with each other like an interlock propeller. Then, sincethe starboard propeller and the port propeller are disposed in parallel,in comparison with the OLP type, risks such as an excessive bearingforce in the rear propeller, expansion of a cavitation range, erosion,can be largely suppressed.

In the propulsion device for the proximity twin-screw vessel having theshaft bracket, provided that propeller diameters of the port propellerand the starboard propeller are Dp, a distance between a centralposition of the port propeller and the starboard propeller and a frontedge of the rudder at a central height of the port propeller and thestarboard propeller may be equal to or less than 1.0 Dp.

According to the above-mentioned configuration, a front edge of therudder can approach the starboard propeller and the port propeller, anda slip stream from the starboard propeller and the port propeller cansecurely abut a rudder surface. Accordingly, control effectiveness ofthe rudder and propulsion performance can be improved.

In the propulsion device for the proximity twin-screw vessel having theshaft bracket, the stern hull may be a stern structure of a single screwvessel type.

According to the above-mentioned configuration, when the stern structureof the single screw vessel type is provided, an effect of theabove-mentioned aspects can be particularly remarkably exhibited. Inaddition, in the stern structure of the single screw vessel type, incomparison with the case in which a skeg serving as the stern structureof the twin-screw vessel type is provided, a longitudinal vortex turninginward in the vicinity of the center in the vessel widthwise directioncan be strengthened, and in the starboard propeller and the portpropeller rotating along the outer track, the flow can be efficientlyrecovered and the propulsion performance can be improved.

In the propulsion device for the proximity twin-screw vessel having theshaft bracket, the shaft bracket may include a shaft support sectionconfigured to rotatably support the propeller shafts of the portpropeller and the starboard propeller, and a strut configured to connectthe shaft support section and the stern hull, and the strut may beformed to provide flows in an opposite direction of a rotationaldirection of the port propeller and the starboard propeller in uppersections of the port propeller and the starboard propeller.

According to the above-mentioned configuration, since flows in anopposite direction of the rotational direction of the port propeller andthe starboard propeller are provided by the strut, a velocity in therotational direction of the flows of the port propeller and thestarboard propeller (10R) is relatively increased. Accordingly, in thestarboard propeller (10R) and the port propeller, forward thrust can befurther exhibited, and the propulsion performance can be improved.

In the propulsion device for the proximity twin-screw vessel having theshaft bracket, the shaft bracket may include a shaft support sectionconfigured to rotatably support the propeller shafts of the portpropeller and the starboard propeller, and a strut configured to connectthe shaft support section and the stern hull, the shaft support sectionmay include one or more fins radially extending from an outercircumferential section of a lower section thereof, and each of the finsmay be formed to provide flows in an opposite direction of a rotationaldirection of the port propeller and the starboard propeller in lowersections of the port propeller and the starboard propeller.

According to the above-mentioned configuration, since the flows in theopposite direction of the rotational direction of the port propeller andthe starboard propeller are provided by the fins, a velocity in therotational direction of the flows of the port propeller and thestarboard propeller is relatively increased. Accordingly in thestarboard propeller and the port propeller, forward thrust can befurther exhibited, and the propulsion performance can be improved.

According to a second aspect of the present invention, a ship includesthe propulsion device for the proximity twin-screw vessel having theshaft bracket according to any one of the above-mentioned aspects.

According to the above-mentioned configuration, as the starboardpropeller and the port propeller are disposed to approach the vicinityof the center in the vessel widthwise direction, the propulsionperformance can be improved. Risks such as generation of a bearingforce, cavitation, erosion, and so on, in the starboard propeller andthe port propeller can be largely suppressed.

Advantageous Effects of Invention

According to the propulsion device for the proximity twin-screw vesselhaving the shaft bracket and the ship of the present invention, thepropulsion performance can be improved while suppressing cavitation,erosion, the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a bottom view showing a configuration of a propulsion devicefor a proximity twin-screw vessel having a shaft bracket of a firstembodiment of the present invention.

FIG. 2 is a side view showing a configuration of the propulsion device.

FIG. 3 is a graph showing a relation between a distance d between thepropeller tips of both of the port and the starboard of the ship, andpropulsion performance of the ship.

FIG. 4 is a conceptual view when the propulsion device is seen from arear side, schematically showing a relation among a starboard propeller,a port propeller and a vortex.

FIG. 5 is a bottom view showing a configuration of a propulsion devicefor a proximity twin-screw vessel having a shaft bracket of a secondembodiment of the present invention.

FIG. 6 is an enlarged view of a major part of FIG. 5, showing across-sectional shape of a strut of a shaft bracket.

FIG. 7 is a view of the propulsion device for the proximity twin-screwvessel having the shaft bracket of the second embodiment of the presentinvention when seen from a rear side.

FIG. 8 is a view of a propulsion device for a proximity twin-screwvessel having a shaft bracket of a third embodiment of the presentinvention when seen from a rear side.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a propulsion device for a proximity twin-screw vesselhaving a shaft bracket and a ship of an embodiment of the presentinvention will be described with reference to the accompanying drawings.

First embodiment

FIG. 1 is a bottom view showing a configuration of a propulsion devicefor a proximity twin-screw vessel having a shaft bracket of a firstembodiment. FIG. 2 is a side view showing the configuration of thepropulsion device.

Here, a twin-screw vessel (a ship, a proximity twin-screw vessel) 1having a stern structure of a single screw vessel type that is a kind ofmulti-screw vessel is exemplarily described as a ship.

As shown in FIG. 1, a propulsion device of the twin-screw vessel 1 ofthe embodiment includes a starboard propeller 10R, a port propeller 10Land a rudder 40.

The starboard propeller 10R is installed under a starboard side of thebottom 4 of the stern hull 3 of the ship, that is, the stern of thehull. The starboard propeller 10R is connected to one end of a starboardpropeller shaft 12R. A starboard main engine 18R is installed at astarboard side in the stern hull 3. The starboard propeller shaft 12Rpasses through the stern hull 3 via a bossing 11R formed in the bottom 4of the ship, and the other end is connected to the starboard main engine18R. The starboard main engine 18R rotates the starboard propeller 10Rvia the starboard propeller shaft 12R.

The port propeller 10L is installed under the port side of the bottom 4of the ship of the stern hull 3. The port propeller 10L is connected toone end of a port propeller shaft 12L. A port main engine 18L isinstalled at the port side in the stern hull 3. The port propeller shaft12L passes through the stern hull 3 via a bossing 11L installed in thebottom 4 of the ship, and the other end is connected to the port mainengine 18L. The port main engine I 8L rotates the port propeller 10L viathe port propeller shaft 12L.

As shown in FIGS. 1 and 2, the starboard propeller shaft 12R and theport propeller shaft 12L have rear end sections protruding rearward fromthe stern hull 3 and rotatably supported by shaft brackets 13R and 13Lin front of the starboard propeller 10R and the port propeller 10L.

The shaft brackets 13R and 13L includes tubular support sections 14R and14L configured to rotatably support the starboard propeller shaft 12Rand the port propeller shaft 12L, and a plurality of struts 15R, 16R,15L and 16L extending upward from the tubular support sections 14R and14L in a V shape and having upper ends connected to the bottom 4 of thestern hull 3.

The starboard propeller 10R and the port propeller 10L are symmetricallydisposed with respect to a center C in a vessel widthwise direction tobe spaced a distance from each other at which the propeller blades donot interfere with each other. That is, the twin-screw vessel 1 is atype in which the starboard propeller 10R and the port propeller 10L aredisposed in parallel, rather than an OLP type or an interlock propellertype.

Here, a distance between the starboard propeller 10R and the portpropeller 10L represents a distance d between propeller tips, which is agap between the outermost circumferential section of the starboardpropeller 10R and the outermost circumferential section of the portpropeller 10L, at the center C side in the vessel widthwise direction.The distance d between the propeller tips may be set to be as small aspossible while still avoiding any risk of contact between the propellerblades such that the starboard propeller 10R and the port propeller 10Lare disposed to approach the vicinity of the center C in the vesselwidthwise direction to capture the longitudinal vortex. The distance dbetween the propeller tips is determined as follows.

That is, since the twin-screw vessel 1 is a type in which the starboardpropeller 10R and the port propeller 10L are arranged in parallel, thedistance d between the propeller tips is set to be larger than 0 in. Thedistance d between the propeller tips may be equal to or larger than 0.1m. This is so that the starboard propeller 10R and the port propeller10L do not interfere with each other even when a machining error or anassembly error is considered.

In addition, the distance d between the propeller tips is preferably setto be equal to or less than 1.0 m, and more preferably equal to or lessthan 0.5 m. This is because reducing the distance d between thepropeller tips as much as possible allows the longitudinal vortex closeto the center C in the vessel widthwise direction to be captured and thepropulsion performance to be further improved.

FIG. 3 is a graph showing a relation between the distance d between thepropeller tips of both of the port and the starboard of the ship, andthe propulsion performance of the ship of the first embodiment of thepresent invention.

In FIG. 3, a lateral axis shows a value of the distance d between thepropeller tips of the starboard propeller 10R and the port propeller10L. A longitudinal axis is a propulsion performance index of the ship,and shows a value standardized by setting the propulsion performance as1.0 when the single screw vessel propelled by a set of the propeller andthe main engine is provided at the same stern hull 3. Here, thepropulsion performance is horsepower performance, and performancebecomes better as horsepower required for outputting the same speed isreduced, i.e., fuel efficiency becomes better. Accordingly, lowernumerical values of the propulsion performance index indicate betterpropulsion performance, and higher numerical values indicate worsepropulsion performance. Accordingly, in order to improve the propulsionperformance in comparison with the single screw vessel, the propulsionperformance should be equal to or less than 1.0. Accordingly, an upperlimit of the distance d between the propeller tips may be set to 1.0 m.

An example of this will be described below. FIG. 4 is a conceptual viewschematically showing a relation among the starboard propeller 10R, theport propeller 10L and the vortex. In FIG. 4, longitudinal vortices V2and V1 are generated in a region 80 in the vicinity of the center C inthe vessel widthwise direction. In order to efficiently recover thelongitudinal vortices V2 and V1 of the region 80 and improve thepropulsion performance, a rotational direction of the starboardpropeller 10R and the port propeller 10L of the twin-screw vesselbecomes outer tracks R2 and R1 that rotate outward from the center C inthe vessel widthwise direction over the starboard propeller 10R and theport propeller 10L.

The starboard propeller 10R and the port propeller 10L can efficientlyrecover the longitudinal vortices V1 and V2 within regions S2 and S1overlapping the region 80. Then, since an area obtained by summing theregion S2 and the region S1 is increased as the distance d between thepropeller tips is reduced, the propulsion performance can be furtherimproved.

In addition, central heights of the starboard propeller 10R and the portpropeller 10L may not be disposed at the same position. However, thecentral heights may be disposed at the same position in consideration ofcontrollability of the twin-screw vessel 1.

In addition, front end sections 9 at the same heights as the starboardpropeller 10R and the port propeller 10L of the stern hull 3 may bedisposed closer to the bow side than the positions of the ends of therotational surfaces of the starboard propeller 10R and the portpropeller 10L near the bow side.

The rudder 40 is installed on the center C in the vessel widthwisedirection in rear of the starboard propeller 10R and the port propeller10L.

The rudder 40 is disposed closer to the rear side (the stern side) thanthe starboard propeller 10R and the port propeller 10L. The rudder 40has a blade-shaped cross-sectional shape, and is attached to a ruddershaft 41 extending from the bottom 4 of the ship of the stern hull 3 ina vertical downward direction. The rudder 40 is rotated about thevertical axis together with the rudder shaft 41, and changes a coursedirection of the twin-screw vessel 1.

Here, a front edge 40 f of the rudder 40, the starboard propeller 10Rand the port propeller 10L may come as close to one another as possible.This is because rapid flows generated by the starboard propeller 10R andthe port propeller 10L enter the rudder 40, and thus the controleffectiveness of the rudder is improved. Specifically, when a propellerdiameter of the starboard propeller 10R and the port propeller 10L isDp, a distance L between a central position Pc of the starboardpropeller 10R and the port propeller 10L and a front edge 40 fp of therudder 40 at a central height Ph of the starboard propeller 10R, and theport propeller 10L may be equal to or less than 1.0 Dp.

Accordingly, according to the propulsion device for the proximitytwin-screw vessel having the shaft bracket and the ship of theabove-mentioned first embodiment, since the starboard propeller 10R andthe port propeller 10L are disposed to approach the vicinity of thecenter C in the vessel widthwise direction, the longitudinal vortex inthe vicinity of the center C in the vessel widthwise direction can beefficiently recovered, and the propulsion performance can be improved.In addition, the starboard propeller 10R and the port propeller 10L donot interfere with each other like the interlock propeller type.Accordingly, the twin-screw vessel 1 can be easily manufactured. Then,since the starboard propeller 10R and the port propeller 10L aredisposed in parallel, in comparison with the OLP type, risks such as anexcessive bearing force of the rear-side propeller, expansion of acavitation range, erosion, can be largely suppressed.

In this way, according to the twin-screw vessel 1, the propulsionperformance can be further improved while suppressing generation ofcavitation, erosion, or the like.

In addition, as propeller shafts 12R and 12L are exposed by setting alength of the bossing 11R and 11L in a lower limit and rear end sectionsthereof are supported by the shaft brackets 13R and 13L, auxiliarysection resistance can be suppressed to be small. This can alsocontribute to improvement of the propulsion performance.

In addition, according to the propulsion device of the twin-screw vessel1, the distance L between the central position Pc of the port propeller10L and the starboard propeller 10R, and the front edge 40 fp of therudder 40 at the central height Ph of the port propeller 10L and thestarboard propeller 10R is set to be equal to or less than 1.0 Dp.Accordingly, the front edge 40 fp of the rudder 40 can approach thestarboard propeller 10R and the port propeller 10L, and a slip streamcan enter the rudder 40 from the starboard propeller 10R and the portpropeller 10L. Accordingly, control effectiveness of the rudder can beimproved.

In addition, according to the propulsion device of the twin-screw vessel1, when the stern hull 3 has a stern structure of the single screwvessel type, the above-mentioned effect can be particularly remarkablyexhibited. Further, the stern structure of the single screw vessel typecan strengthen the longitudinal vortex turning inward in the vicinity ofthe center C in the vessel widthwise direction in comparison with thecase in which a skeg serving as the stern structure of the twin-screwvessel type is provided, and in the starboard propeller 10R and the portpropeller 10L that rotate along the outer track, the flow can beefficiently recovered to improve the propulsion performance.

Modified Example of the First Embodiment

Further, in the first embodiment, while the stern hull 3 of thetwin-screw vessel 1 has the stern structure of the single screw vesseltype, the embodiment is not limited thereto. In the stern hull 3, theskeg extending along the center C in the vessel widthwise direction maybe provided in front of the rudder 40.

Second Embodiment

Next, a second embodiment of the propulsion device for the proximitytwin-screw vessel having the shaft bracket and the ship according to thepresent invention will be described. Since the second embodiment to bedescribed below is different from the first embodiment only in theconfigurations of the shaft brackets 13R and 13L, the same components asthe first embodiment are designated by the same reference numerals, andoverlapping description thereof will be omitted.

FIG. 5 is a bottom view showing a configuration of the propulsion deviceof the proximity twin-screw vessel having the shaft bracket of thesecond embodiment of the present invention. FIG. 6 is an enlarged viewof a major part of FIG. 5, showing a cross-sectional shape of a strut ofa shaft bracket. FIG. 7 is a view of the propulsion device of theproximity twin-screw vessel having the shaft bracket of the secondembodiment of the present invention when seen from a rear side.

As shown in FIGS. 5, 6 and 7, the twin-screw vessel 1 according to theembodiment includes the starboard propeller 10R, the port propeller 10Land the rudder 40 provided with the same configuration as in the firstembodiment.

The starboard propeller shaft 12R and the port propeller shaft 12L arerotatably supported by the shaft brackets 13R and 13L in front of thestarboard propeller 10R and the port propeller 10L. Further, in theembodiment, struts 25R, 26R, 25L and 26L of the shaft brackets 13R and13L have a blade-shaped cross-sectional shape perpendicular to adirection extending from the bottom 4 of the ship toward the tubularsupport sections 14R and 14L. Further, the struts 25R, 26R, 25L and 26Lare formed to provide flows in an opposite direction of the rotationaldirection of the starboard propeller 10R and the port propeller 10L inthe upper sections of the starboard propeller 10R and the port propeller10L. That is, the starboard propeller 10R and the port propeller 10L arerotated along the outer tracks R2 and R1 outward from the center C inthe vessel widthwise direction over the starboard propeller 10R and theport propeller 10L. Here, the struts 25R, 26R, 25L and 26L are installedto generate flows FR1 and FL1 from the outside in the vessel widthwisedirection toward the center C in the vessel widthwise direction over thestarboard propeller 10R and the port propeller 10L. Specifically, thestruts 25R, 26R, 25L and 26L are formed to be inclined from front edgesections 25 f and 26 f toward rear edge sections 25 r and 26 r togradually approach the center C in the vessel widthwise direction from apropeller shaft direction Sp.

Accordingly, according to the propulsion device for the proximitytwin-screw vessel having the shaft bracket and the ship of theabove-mentioned second embodiment, the struts 25R, 26R, 25L and 26L ofthe shaft brackets 13R and 13L have a blade-shaped cross-sectionalshape, and the flows FR1 and FL1 from the outside in the vesselwidthwise direction opposite to the rotational direction of thestarboard propeller 10R and the port propeller 10L are provided in theupper sections of the starboard propeller 10R and the port propeller 10Lrotating along the outer tracks R2 and R1 toward the center C in thevessel widthwise direction. Accordingly, a velocity in the rotationaldirection of the flows of the port propeller 10L and the starboardpropeller 10R is relatively increased. As a result, the slip stream thatpasses the struts 25R, 26R, 25L and 26L of the shaft brackets 13R and13L can be efficiently recovered by the starboard propeller 10R and theport propeller 10L, and the propulsion performance can be improved.

In addition, according to the propulsion device for the twin-screwvessel 1, like the first embodiment, since the starboard propeller 10Rand the port propeller 10L are disposed in the vicinity of the center Cin the vessel widthwise direction, the longitudinal vortex in thevicinity of the center C in the vessel widthwise direction can beefficiently recovered, and the propulsion performance can be improved.In addition, the starboard propeller 10R and the port propeller 10L donot interfere with each other like the interlock propeller type.Accordingly, the twin-screw vessel 1 can be easily manufactured. Then,since the starboard propeller 10R and the port propeller 10L aredisposed in parallel, in comparison with the OLP type, risks such as anexcessive bearing force in the rear-side propeller, expansion of acavitation range, erosion, can be largely suppressed.

In this way, according to the twin-screw vessel 1, the propulsionperformance can be improved while suppressing cavitation, erosion, orthe like.

As shown in FIGS. 5 and 6, in the configuration of the embodiment, thepropeller shaft direction Sp may be inclined with respect to the centerC in the vessel widthwise direction, and the starboard propeller shaft12R and the port propeller shaft 12L or the port main engine 18L and thestarboard main engine 18R may be disposed such that a distance betweenthe starboard propeller shaft 12R and the port propeller shaft 12L isgradually reduced toward the rear of the hull to have a horizontal rake.

Third embodiment

Next, a third embodiment of the propulsion device for the proximitytwin-screw vessel having the shaft bracket and the ship according to thepresent invention will be described. Since the third embodiment to bedescribed below is different from the second embodiment only in theconfigurations of the shaft brackets 13R and 13L, the same components asthe second embodiment are designated by the same reference numerals, andoverlapping description thereof will be omitted.

FIG. 8 is a view of the propulsion device of the proximity twin-screwvessel having the shaft bracket of the third embodiment of the presentinvention, when seen from a rear side.

As shown in FIG. 8, the twin-screw vessel 1 according to the embodimentincludes the starboard propeller 10R, the port propeller 10L and therudder 40 provided with the same configuration as in the secondembodiment.

The starboard propeller shaft 12R and the port propeller shaft 12L arerotatably supported by the shaft brackets 13R and 13L in front of thestarboard propeller 10R and the port propeller 10L. In the embodiment,the tubular support sections 14R and 14L of the shaft brackets 13R and13L include one or more (in the embodiment, four) fins 45 extending in aradial direction and formed at outer circumferential sections of lowersections thereof.

The fins 45 have a blade-shaped cross-sectional shape perpendicular to adirection extending from the tubular support sections 14R and 14L towardthe outer circumference. Further, the fins 45 are formed to provideflows in an opposite direction of the rotational direction of thestarboard propeller 10R and the port propeller 10L in the lower sectionsof the starboard propeller 10R and the port propeller 10L. That is, thestarboard propeller 10R and the port propeller 10L are rotated from theoutside toward the center C in the vessel widthwise direction under thestarboard propeller 10R and the port propeller 10L. Here, the fins 45are formed to generate flows FR2 and FL2 from the center C in the vesselwidthwise direction outward in the vessel widthwise direction under thestarboard propeller 10R and the port propeller 10L. Specifically, thefins 45 are formed to be inclined from a front edge section 45 f towarda rear edge section 45 r and to gradually go away from the center C inthe vessel widthwise direction outward in the vessel widthwise directionunder the starboard propeller 10R and the port propeller 10L.

Accordingly, according to the propulsion device for the proximitytwin-screw vessel having the shaft bracket and the ship of theabove-mentioned third embodiment, the fins 45 installed at the shaftbrackets 13R and 13L have a blade-shaped cross-sectional shape, and theflows FR2 and FL2 having a vortex shape from the center C in the vesselwidthwise direction in an opposite direction of the rotational directionof the starboard propeller 10R and the port propeller 10L outward in thevessel widthwise direction can be provided in the lower sections of thestarboard propeller 10R and the port propeller 10L. Accordingly, avelocity in the rotational direction of the flows of the port propeller10L and the starboard propeller 10R is relatively increased. As aresult, the slip stream that passes the fins 45 of the shaft brackets13R and 13L can be efficiently recovered by the starboard propeller 10Rand the port propeller 10L, and the propulsion performance can beimproved.

In addition, according to the propulsion device for the twin-screwvessel 1, like the first and second embodiments, since the starboardpropeller 10R and the port propeller 10L are disposed to approach thevicinity of the center C in the vessel widthwise direction, thelongitudinal vortex in the vicinity of the center C in the vesselwidthwise direction can be efficiently recovered, and the propulsionperformance can be improved. In addition, the starboard propeller 10Rand the port propeller 10L do not interfere with each other like theinterlock propeller type. Accordingly, the twin-screw vessel 1 can beeasily manufactured. Then, since the starboard propeller 10R and theport propeller 10L are disposed in parallel, in comparison with the OLPtype, risks such as an excessive bearing force in the rear-sidepropeller, expansion of a cavitation range, erosion, can be largelysuppressed.

in this way, according to the twin-screw vessel 1, the propulsionperformance can be improved while suppressing cavitation, erosion, orthe like.

Further, in the third embodiment, while the same struts 25R, 26R, 25Land 26L as in the second embodiment are provided, the embodiment is notlimited thereto but the same struts 15R, 16R, 15L and 16L as in thefirst embodiment may be provided.

Other Modified Examples

Further, the present invention is not limited to the above-mentionedembodiments but various modifications may be added to theabove-mentioned embodiments without departing from the scope of thepresent invention. That is, the specific shapes, configurations, and soon, are exemplarily mentioned in the embodiments and may beappropriately modified.

REFERENCE SIGNS LIST

-   1 twin-screw vessel (ship, proximity twin-screw vessel)-   3 stern hull-   4 bottom of ship-   9 front end section-   10L port propeller-   10R starboard propeller-   11L, 11R bossing-   12L port propeller shaft-   12R starboard propeller shaft-   13R, 13L shaft bracket-   14R, 14L tubular support section-   15R, 15L, 16R, 16L, 25R, 25L, 26R, 26L strut-   18L port main engine-   18R starboard main engine-   40 rudder-   40 f, 40 fp front edge-   41 rudder shaft-   45 tin-   80 region-   C center of vessel widthwise direction-   D distance between propeller tips-   Ls reference line-   V1, V2 longitudinal vortex

1. A propulsion device for a proximity twin-screw vessel having a shaftbracket, the propulsion device comprising: a port propeller and astarboard propeller installed at a stern hull; one rudder disposed at acenter in a vessel widthwise direction of the stern hull or two ruddersconstituted by a port rudder and a starboard rudder in rear of the portpropeller and the starboard propeller; and shaft brackets installed infront of the port propeller and the starboard propeller, respectively,and configured to rotatably support propeller shafts of the portpropeller and the starboard propeller, wherein a distance between a tipend of a propeller blade of the port propeller and a tip end of apropeller blade of the starboard propeller at a center in the vesselwidthwise direction is larger than 0 m and equal to or smaller than 1.0m, and a rotational direction of the port propeller and the starboardpropeller becomes an outer track rotating from the center in the vesselwidthwise direction toward the outside over the port propeller and thestarboard propeller.
 2. The propulsion device for the proximitytwin-screw vessel having the shaft bracket according to claim 1,wherein, provided that propeller diameters of the port propeller and thestarboard propeller are Dp, a distance between a central position of theport propeller and the starboard propeller and a front edge of therudder at a central height of the port propeller and the starboardpropeller is equal to or less than 1.0 Dp.
 3. The propulsion device forthe proximity twin-screw vessel having the shaft bracket according toclaim 1, wherein the stern hull is a stern structure of a single screwvessel type.
 4. The propulsion device for the proximity twin-screwvessel having the shaft bracket according to claim 1, wherein the shaftbracket comprises a shaft support section configured to rotatablysupport the propeller shafts of the port propeller and the starboardpropeller, and a strut configured to connect the shaft support sectionand the stern hull, and the strut is formed to provide flows in anopposite direction of a rotational direction of the port propeller andthe starboard propeller in upper sections of the port propeller and thestarboard propeller.
 5. The propulsion device of the proximitytwin-screw vessel having the shaft bracket according to claim 1, whereinthe shaft bracket comprises a shaft support section configured torotatably support the propeller shafts of the port propeller and thestarboard propeller, and a strut configured to connect the shaft supportsection and the stern hull, and the shaft support section comprises oneor more fins radially extending from an outer circumferential section ofa lower section thereof, and each of the fins is formed to provide flowsin an opposite direction of a rotational direction of the port propellerand the starboard propeller in lower sections of the port propeller andthe starboard propeller.
 6. A ship comprising the propulsion device ofthe proximity twin-screw vessel having the shaft bracket according toclaim 1.